This invention relates in general to hemodialysis. It relates, more particularly, to hemodialysis catheters.
Hemodialysis, as practiced today, normally employs one of two types of catheter to remove blood from the patient for processing and return processed blood to the patient. Most commonly, a catheter tube containing two lumens is used, each lumen having a generally semi-cylindrical or D-shape configuration. This type of catheter is frequently referred to as a dual lumen catheter. Alternatively, two tubes, each with a full cylindrical configuration, are used separately to remove blood for dialysis and return the processed blood.
Flow rates possible with conventional dual lumen catheters are usually lower than those achievable where separate tubes are used to remove blood from a vein for dialysis and then return processed blood back to the vein.
Thus, the use of two tubes has become more and more popular as the capacity (maximum flow rate) of hemodialysis membranes has increased.
Hemodialysis membranes are now able to process blood at over 500 ml of flow per minute. Even higher processing rates are foreseeable. However, problems occur with both the line introducing purified blood back into the vein (the venous or outflow line) and the line removing blood for purification (the arterial or intake line) at flow rates above 300 ml per minute. A high flow rate from the venous line may cause whipping or xe2x80x9cfirehosingxe2x80x9d of the tip in the vein with consequent damage to the vein lining. A corresponding high flow rate into the arterial line may cause the port to be sucked into the vein wall, resulting in occlusion. It should be understood, of course, that both lines normally access the superior vena cava and the designations are used for differentiation purposes.
Speed of flow through a catheter lumen, whether it be in a single lumen or a dual lumen catheter, is controlled by a number of factors including the smoothness of the wall surface, the internal diameter or cross-sectional area of the tube lumen, and the length of the tube lumen. The most important factor is the cross-sectional area of the tube lumen. The force or speed of the fluid flow in a tube lumen for a given cross-sectional area is controlled by the external pumping force, of course. This is a positive pressure pushing processed blood through the venous lumen and a negative (suction) pressure pulling unprocessed blood through the arterial lumen.
Problems encountered in providing for a high flow rate through a catheter are magnified in a dual lumen catheter construction. Because each of the lumens in a dual lumen catheter normally has a D-shape, it has been assumed that flow rates are limited. Furthermore, such dual lumen catheters are, to a great extent, catheters with a main port which opens at the end of a lumen substantially on the axis of the lumen. Thus, xe2x80x9cfirehosingxe2x80x9d frequently results. Fire-hosing may damage the vein wall, triggering the build-up of fibrin on the catheter tip. Fibrin build-up may result in port occlusion.
There are dual lumen catheters which utilize side ports for both outflow and inflow. An example is the catheter disclosed in the Cruz et al. U.S. Pat. No. 5,571,093. However, such catheters have not been entirely successful in solving problems related to hemodialysis with dual lumen catheters, e.g., high incidences of catheter port occlusion as well as some degree of fire-hosing.
Catheters of almost all types are also pliable so that they do not damage body tissue when they are in-situ. Pliability can create a problem during insertion, however, because the catheters can kink when they meet resistance. Thus, there is often a need for a certain amount of stiffness so that the catheters can be directed within body vessels or cavities. There are currently two methods of providing this stiffness; stylets and guide wires.
A stylet can be a single or a twisted wire with a blunt end that is inserted into the catheter to make it stiff. The stylet is often used with bullet nose catheters and maintains its position within the catheter as the catheter is inserted. The stiffened catheter is advanced into the blood vessel with the stylet.
In contrast, guide wires are used to both stiffen the catheter and to provide a guide for the insertion. Commonly, the guide wire is inserted into the blood vessel before the catheter. The catheter is then inserted into the blood vessel over the wire, and follows the wire as it travels inside the vessel. Guide wires are most often utilized with catheters that are inserted deep into the body, such as with central venous catheters that are inserted into the heart. The thin guide wire more easily makes the bends and turns necessary for this type of placement.
In guide wire insertion where the catheter must be inserted over the guide wire, catheters with open ends are normally utilized to permit passage of the guide wire. These catheters are more likely to cause damage to body tissue during insertion than bullet nose catheters, for example, because of their flat ends and side edges. Open ended catheters are also more likely to damage tissue than bullet nose catheters while in-situ. Nevertheless, the need for deep catheter insertion has heretofore made guide wire insertion of open-ended catheters the accepted procedure in spite of the disadvantage of their flat or blunt end design.
As an alternative, bullet nose catheters have occasionally been used with guide wires in some applications by incorporating a small hole through the nose for the wire to pass through. This approach has generally been found undesirable, however, because the hole in the bullet nose can later collect particulate matter and be a focal point for infection.
An object of the invention is to provide an improved dual lumen hemodialysis catheter.
Another object is to provide a dual lumen hemodialysis catheter which accommodates flow rates substantially as high as the latest separate lumen catheters.
Still another object is to provide a dual lumen hemodialysis catheter which is capable of returning processed blood to the patient at high flow rates without harmful firehosing of the catheter tip.
Yet another object is to provide a dual lumen hemodialysis catheter which permits high flow rates while minimizing trauma and potential red cell damage so as to substantially avoid clotting.
A further object is to provide a dual lumen hemodialysis catheter which substantially reduces the incidence of port occlusion.
Still a further object is to provide a dual lumen hemodialysis catheter in which occlusion of the return line port is substantially avoided regardless of the flow rate.
Still a further object is to provide a dual lumen hemodialysis catheter which facilitates reversal of the venous and arterial lines to relieve port occlusion without increasing the potential for mixing of dialyzed blood with blood being removed for dialysis
Another object of the invention is to provide an improved bullet nose bolus for use on catheters ranging in size from 3 French to 22 French in any medical application.
A further object is to provide a bullet nose bolus that protects the leading edge of the catheter outflow or inflow port from rubbing against the vessel wall.
Another object is to provide a bullet nose bolus for a catheter that will not kink during insertion.
Another object of the present invention is to provide an improved catheter for use with a guidewire.
Still another object is to provide a bullet nose bolus for a catheter which is compatible with a guide wire yet does not require an axially extending hole through the nose.
Another object is to provide a bullet nose bolus for a catheter that can be inserted simultaneously with a guide wire through a flexible introducer sheath that is essentially the same size as the catheter itself.
Another object is to provide a bullet nose bolus for a catheter that follows a guide wire through bends in a patient""s vein and turns without causing increased resistance to passage through the vein.
Another object is to provide a bullet nose bolus that always presents a rounded surface to the vein wall, even when the catheter is following a guide wire around a bend.
Another object is to provide a bolus with a nose which is designed to flex away from the guide wire in only one direction.
The foregoing and other objects are realized in accord with the present invention by providing a dual lumen hemodialysis catheter including a bullet-nose bolus having a radially opening outflow or venous port and a radially opening intake or arterial port The arterial port is circumferentially displaced 180xc2x0 around the bolus from the venous port.
The venous port opens radially through the bolus immediately behind its bullet nose. The D-shape venous lumen in the catheter tube communicates with a corresponding D-shape venous passage in the body of the bolus. That D-shape venous passage transitions into a circular cross-section venous passage before reaching the venous port, while increasing in cross-sectional area from the D-shape passage to the circular passage.
The arterial port is axially displaced from the venous port and opens radially through the bolus immediately behind the venous port, albeit 180xc2x0 displaced therefrom. The arterial port communicates directly with a corresponding D-shape arterial passage in the body of the bolus.
In front of the arterial port and opposite the venous port, the profile of the bolus curves in an arc toward the side of the bolus in which the venous port is disposed, creating a stiffening arch in the passage section opposite the venous port. From the trailing edge of the venous port forward, the passage section and the nose section are effectively inclined to the longitudinal axis of the bolus and tube, and toward the venous port side of the bolus. The bullet nose of the nose section is thus offset from the axis of the bolus toward the venous port.
The opposite side surfaces of the bolus, proceeding forward from the mid-point of the venous port, also taper inwardly in converging arcs to the bullet nose section. Thus, the bolus nose section is both narrower in width and thinner in height than the trailing remainder of the bolus and the catheter tube itself.
Where the passage section joins the nose section of the bolus, on a plane extending transversely through the bolus in front of the venous port, the nose section has a maximum thickness in the plane on a line passing through the bolus axis and the center of the venous port. The thickness of the nose section is 20% to 25% less than the diameter of the catheter tube itself. The plane is inclined forwardly away from the port at an angle corresponding to the angle of inclination of the curving passage section toward the bolus axis.
The nose section of the bolus, being not as thick as the rest of the bolus but displaced radially to the venous port side of the longitudinal axis of the bolus passage section and catheter tube, is in a position wherein a portion of its outermost periphery is tangent to an imaginary cylinder containing the outer surface of the bolus passage section at the trailing edge of the venous port. This offset nose configuration prevents the vein wall from wrapping around the trailing edge of the port and being abraded thereby.
The stiffening arch defined in the bolus opposite the venous port inhibits folding of the bolus at the venous port during insertion of the catheter. Immediately opposite the arterial port, another stiffening arch is also formed in the bolus. The arch extends along that side of the bolus from a point radially aligned with the trailing edge of the arterial port to the trailing edge of the venous port. This arch inhibits folding of the bolus around the arterial port.
The catheter of the invention, with its novel bolus, lends itself ideally to insertion in a patient""s vein over a guide wire. When inserted through the vein the bullet nose section flexes radially outwardly in a plane passing through the bolus axis and both ports under the influence of the guide wire. Because the nose section has a smaller thickness in that plane than the rest of the bolus and the tube, however, it is not forced outside the imaginary cylinder of the catheter. This makes for ease of insertion.